Antichafing strip for shaving equipment head and shaving equipment head comprising same

ABSTRACT

The anti-friction strip of the invention for a discardable razor is obtained by extruding a polymer mixture comprising an insoluble polymer material and polyethylene oxide. It has an initial coefficient of dynamic friction (K D ) of the order of or less than 0.2. The mixture for extrusion includes, as its polyethylene oxide, only a substance whose mean molecular weight is greater than 3.5 million. The strip is preferably obtained by extruding a mixture comprising polystyrene and polyethylene oxide having a mean molecular weight greater than 4 million, and in particular a single polyethylene oxide having a molecular weight greater than 7 million. The invention also provides a shaving head having the above-specified anti-friction strip fixed thereto by ultrasonic welding.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to the field of shaving by mechanicalmeans using a discardable razor; it relates more particularly to anauxiliary shaving article in the form of a strip and referred to as a“strip”, which is fixed on the shaving head, preferably in the vicinityof the shaving blades, and which contains at least oneshaving-assistance component that is soluble in water.

2. Description of the Related Art

When the razor is used, the user dips the shaving head in hot water,thereby making a portion of the shaving-assistance components)accessible and leachable, which components come into contact with theskin on each pass of the razor.

In U.S. Pat. No. 4,170,821 to Booth, the auxiliary shaving articleproposed is combined with a micro-encapsulating or micro-porouswater-soluble solid structure for retaining the shaving-assistancecomponent which can be selected from a list of substances comprising alubricant for reducing the effect of friction between the razor and theskin, an agent for reducing rubbing between the razor and the skin, anagent suitable for modifying hair structure, a cleansing agent, apharmaceutical agent, a cosmetic agent, and a coagulation agent. As anexample of a lubricant for reducing the effect of friction between therazor and the skin, U.S. Pat. No. 4,170,821 cites a micro-encapsulatedsilicone-based oil, and as an example of an agent for reducing rubbingbetween the razor and the skin, that document cites an oxide ofpolyethylene having molecular weight lying in the range 100,000 to6,000,000, a non-ionic polyacrylamide, and a natural polysaccharidederived from plant matter such as guar gum.

In document EP-B-0 1 184 440, provision is made to form an auxiliaryshaving article in the form of a strip by extruding a mixture of watersoluble and insoluble polymer materials. That document gives a list ofwater soluble polymers comprising polyethylene oxide,poly-vinylpyrrolidone, polyacrylamides, hydroxypropyl-cellulose,polyvinylimidazoline, and hydroxyethyl poly-methacrylate. In aparticular embodiment, the mixture for forming said strip by extrusionis made up of 20% by weight water insoluble polystyrene and 80% byweight of a mixture of polyethylene oxide comprising 60% “coagulatingpolyox” polyethylene oxide of molecular mass equal to 5,000,000, and 40%“WSR N-750 polyox” polyethylene oxide of molecular mass equal to300,000. No explanation is given in that document concerning theadvantage of mixing those two types of polyethylene oxide together,other than for obtaining a mean molecular weight of about 3.5 millionfor the polyethylene oxide in the final mixture.

In document EP-B-0 550 605, the mixture for forming the auxiliaryshaving article by extrusion in the form of a strip contains, inaddition to the water soluble and insoluble materials, an agent of lowmolecular weight for amplifying the release of the water soluble polymermaterial making up the shaving-assistance component. Amongst all of thepossible examples, that document cites polyethylene oxide as ashaving-assistance component which can be leached by water, andpolyethylene glycol as an agent for amplifying release. Incharacteristic manner, according to that document EP-B-0 550 605, themixture for forming the auxiliary shaving article by extrusion in theform of a strip comprises 20% to 60% by weight of insoluble polymermaterial that forms the matrix of the strip, 20% to 75% by weight ofwater soluble polymer material that constitutes the water-leachableshaving-assistance component, and 5% to 20% by weight of agent foramplifying release. In all of the examples cited in that document,exactly the same mixture of two types of polyethylene oxide is to befound as already described in prior document EP-B-0 184 440, i.e. 60% byweight of coagulating polyox and 40% by weight of WSR N-750 polyox. Inthe examples cited, the agent for amplifying release is a polyethyleneglycol of molecular weight lying in the range 4,500 to 20,000. Theintended purpose of having the release-amplifying agent present is tomake it possible to maintain a sufficient quantity of insoluble polymerfor retaining sufficient mechanical strength in the extruded strip bothon initial manufacture and assembly, and after a significant quantity ofwater soluble material has already been leached, while still making itpossible for a sufficient quantity of water soluble shaving component tobe released to provide effective shaving assistance throughout the totaluseful lifetime intended for the blade or blades.

In that document EP-B-0 550 605, no explanation is given concerning thereasons which enable certain specified agents of low molecular weight toamplify release of the shaving-assistance component, i.e. ethyleneglycol, methoxy polyethylene glycol, methyl-cellulose, andcarboxypolymethylene. It should be observed that those four examples arethe only examples mentioned in that document, and that they all relateto the above-mentioned mixture of polyethylene oxide and the addedpolyethylene glycol. It should be recalled that polyethylene oxide andpolyethylene glycol have the same general formula, differing only inmethod of manufacture and mean molecular weight. The term “polyethyleneglycol” is used to designate a compound whose molecular weight isgenerally less than 20,000. The term “polyethylene oxide” is used todesignate a compound whose main molecular weight is greater than100,000, it being understood that a very wide variety of products areavailable on the market, having the general formula of polyethyleneoxide, with mean molecular weights lying in the range 100,000 to8,000,000.

Thus, according to the Applicant, it can be thought that polyethyleneglycol is used in document EP B 0 550 605 also as a shaving-assistancecomponent, in addition to the low molecular weight polyethylene oxide(WSR N-750 polyox) so as to obtain sufficient release ofshaving-assistance components during the lifetime of the discardableshaving head.

Thus, present trends in this field are towards releasing a large amountof shaving-assistance soluble component, in particular polyethyleneoxide which is preferably associated with polyethylene glycol.Nevertheless, because a large amount is released, the component remainspresent on surfaces of the skin that have already been shaved, and canform a film by drying out. To avoid that drawback, it is necessary forthe user to wash after shaving. However, depending on the quality of thewater available, this removal is not always satisfactory and a stickyfeeling can remain on the skin. If all or some of the soluble componentremains on the skin, that can be a source of irritation, particularlyfor sensitive skins.

To mitigate those drawbacks, proposals have already been made indocument EP-B-0 321 679, for a solution that is different in principlesince it avoids the use of a soluble polymer by proposing to implement axerophilic gel as the anti-friction agent which, while absorbing wateras a dispersing agent, becomes transformed into a lyophilic gel havingvery great aptitude for sliding on the skin of the user, with acoefficient of friction μ of less than 0.25. By adding the dispersionagent, e.g. water, the xerophilic gel becomes transformed once more intoa lyophilic gel by swelling, with its outside surface becoming slipperyand presenting a low coefficient of friction. During this stage, thecolloidal substance forming the-lattice of the lyophilic gel does notpass into solution, thereby making it possible to avoid forming on theskin a film constituted by a shaving-assistance component extracted fromthe strip, as was the case in the previously-cited documents.

Nevertheless, according to the teaching of that document EP-B-0 321 679,it is necessary to put the coating that forms the xerophilic gel on asupport strip in order to constitute the anti-friction strip proper forplacing on the shaving head. The materials recommended for forming thexerophilic gel do not withstand temperatures that would make it possibleto consider fabricating the anti-friction strip by extrusion.

SUMMARY OF INVENTION

The object of the Applicant is to propose another solution that does notmake use of a xerophilic gel, that makes it possible to obtain ananti-friction strip by extrusion, while enhancing ability to slide onthe skin of the user, and without running the risk of forming a film ofthe soluble component on the user's skin.

DETAILED DESCRIPTION OF INVENTION

This object is achieved in full by the anti-friction strip fordiscardable razors of the invention which, in conventional manner, isobtained by extruding a polymer mixture of an insoluble polymer materialand of polyethylene oxide as the soluble polymer material. In mannercharacteristic of the invention, said strip is characterized by aninitial coefficient of dynamic friction (K_(D)) of the order of or lessthan 0.2, and by the fact that the mixture to be extruded comprises, asits polyethylene oxide, only a substance whose mean molecular weight isgreater than 3.5 million.

The Applicant has observed that the presence of polyethylene oxide oflower molecular weight, even when mixed with polyethylene oxide ofhigher molecular weight, leads to an increase in the coefficient ofdynamic friction.

It also turns out that the greater the molecular weight of thepolyethylene oxide, the smaller its solubility in water. Thus, with apolyethylene oxide of molecular weight greater than 3.5 million, releaseis obtained that is relatively low compared with the figures given indocuments EP-B-0 184 440 and EP-B-0 550 605. The risk of skin irritationor of the sensation of slippery skin is thus greatly reduced or eveneliminated by this fact.

During comparative shaving tests, the Applicant has also observedanother significant technical advantage in using only a polyethyleneoxide of high molecular weight in the mixture, namely that of retainingsliding capacity for the anti-friction strip which remains substantiallyconstant or which varies relatively little during a series of shavesusing the same strip. By way of comparison, an anti-friction stripincluding polyethylene oxide of lower molecular weight presents asignificant drop in its sliding capacity after two or three shaves,thereby giving rise to a sensation that is quite disagreeable for theuser.

Preferably, with reference to this technical advantage, theanti-friction strip is obtained by extruding a mixture of polystyreneand a polyethylene oxide of mean molecular weight that is greater than 4million.

Another problem which the Applicant has sought to resolve lies in fixingthe anti-friction strip to the shaving head. In document FR-A-2 410 541,the strip is fixed to the shaving head, preferably in a housing providedfor that purpose. No indication is given as to how it is fixed therein.In document EP-B-0 184 440, the strip has a special profile, and it islocked in position by structural elements on the shaving head. Thatsolution makes fabrication of the head more complex. In document EP-B-0550 605, the anti-friction strip is fixed by means of adhesive in ahollow portion of the shaving head. That solution requires the use of anadhesive that sets particularly quickly if a high rate of manufacturingthroughput is to be obtained.

In order to fix the anti-friction strip on the shaving head, theApplicant proposes the well-known technique of ultrasonic welding. Thistechnique consists in creating vibratory conditions under the action ofultrasound that make it possible, locally, to raise the temperature oftwo touching plastics materials so as to obtain localizedinterpenetration of the two materials.

The Applicant has observed that by using the ultrasonic weldingtechnique with an anti-friction strip of polyethylene oxide having amolecular weight greater than 3.5 million makes it possible to obtain aweld that is of good quality. A weld between a first plastics materialacting as a base and a plastics material applied thereto is said to beof “good quality” when breaking the weld by applying mechanical stressgives rise to breakage taking place for the most part in the basematerial or in the material applied thereto, but not within the weldproper. Material is, so to speak, torn beyond the zone in which the twomaterials have interpenetrated.

Best results have been obtained with an anti-friction strip made byextruding a mixture of poly-ethylene and a polyethylene oxide having amean molecular weight in excess of 7 million, which is fixed byultrasonic welding onto a portion of a shaving head that is made ofpolystyrene.

The present invention will be better understood on reading the followingdescription of an embodiment of an anti-friction strip having a lowdynamic friction coefficient, made by extruding a mixture of polystyreneand of polyethylene oxide having a mean molecular weight greater than3.5 million, and shown in the sole figure of the accompanying drawingwhich is a diagram of test apparatus for determining the coefficient ofdynamic friction.

To determine the slidability of the anti-friction strip of theinvention, the Applicant has adapted registered French standard NFT54-112. The purpose of that standard is to measure static and dynamiccoefficients of friction between plastics sheets when sliding on oneanother or on other substances. In the present case, the first plasticssheet is constituted by the anti-friction strip of the invention, andthe second sheet, referred to below as the “sliding track”, is made of amaterial whose characteristics are close to those of skin, e.g. a sheetof polyurethane, a covering of polyurethane and polyester (productreferenced 4PE100/B09T, sold by Catry), or a sheet of acid catalysedmelamine (sold under the trademark Velleda). Naturally the exact valueof the coefficient of dynamic friction is a function of the materialused for the sliding track.

The coefficient of dynamic friction (K_(D)) is the ratio of the tractionforce that needs to be exerted to maintain sliding between the twosurfaces over the normal force urging the two surfaces against eachother. To calculate this coefficient, the force required for startingdisplacement and the force required for maintaining displacement aremeasured relative to each other when the two materials are in contactand the contact pressure between the two materials is kept constantduring the test.

The apparatus 1 implemented for performing this test was constituted bya horizontal support 2 which is designed to support the sliding track 3,e.g. a sheet of polyurethane that was 30 cm long and 15 cm wide,together with a steel slug 4 having a mass of 198 g, a length of 6.35cm, and a width of 3.4 cm. A sample 9 of anti-friction strip to betested was placed beneath the slug 4 in contact with the sliding track3. The slug 4 was pulled by a cable 5 connected to a dynamometer 6, adifflector pulley 7 enabling the slug 4 to be moved horizontally. Thesupport 2 constituted the bottom of a vessel 8 that was thermostaticallycontrolled and that contained water heated to 42° C., the quantity ofsaid water being sufficient to form a film between the sliding track 3and the sample of anti-friction strip 9 under test.

The slug was moved together with its sample in rectilinear manner alongthe sliding track at a speed of 150 mm per minute ±15 mm per minute overa distance of 12 cm. Ten tests were performed per sample. The mean forcenecessary for maintaining displacement of the slug 4 was measured. Thecoefficient of dynamic friction (K_(D)) is the ratio of that force overthe weight of the assembly constituted by the slug 4 plus the sample 9.

The value of the dynamic coefficient (K_(D)) in question is the initialvalue obtained during the first test. The value of the coefficientvaried when performing a series of tests separated by periods duringwhich the strip was dried. It was also observed that it varied lesswhen, after ten tests had been performed so that a mean could beobtained, the strip was rinsed abundantly. Similarly, it was preferableto clean or even replace the sliding track between two tests.

By implementing the above method, the Applicant performed comparativetests between anti-friction strips, all made by extruding a mixture ofpolystyrene and polyethylene oxide of various molecular weights.

All of the tests performed showed that the presence in the mixture ofpolyethylene oxide of low molecular weight, and in particular about300,000, on its own or in the presence of polyethylene glycol, givesrise to a sticking phenomenon that impedes sliding.

In contrast, in accordance with the invention, initial coefficients ofdynamic friction of the order of or less than 0.2 were obtained by usingpolyethylene oxides having a mean molecular weight greater than 3.5million, which coefficients characterize good sliding without thesticking phenomenon.

Comparative tests that were more subjective but closer to shavingconditions were also developed by the Applicant. The two anti-frictionstrips to be compared were stuck to a support plate, with the two stripsbeing parallel and spaced apart from each other by a distance of abouttwo to three centimeters. The tests comprised two operations that wererepeated several times in succession and then the set of tests wasrepeated on several days in a row: the first operation consisted inplunging the plate into warm water (about 40° C. to 42° C.) thussimulating putting the razor under hot water from the tap; the secondconsisted in rubbing both strips simultaneously against two fingers ofthe same hand, thus simulating a shaving sequence. The various timesrequired for each operation were given to each test. In a first example,the first operation lasted 15 seconds and the second 1 minute, with bothoperations being performed in succession, twice in all. In the secondexample, the first operation lasted 5 seconds and the second 30 seconds,both operations being performed in succession four times in all. The setconstituted by repeating those two operations was performed several daysin a row, e.g. 6 or 7 days, simulating the lifetime of a discardablerazor.

The sliding sensation perceived simultaneously on the two fingers madeit possible to classify the strips relative to each other, in terms ofsliding ability, and to assess the difference in sliding between the twostrips. In particular, by means of those tests, which reproduced realshaving conditions quite closely, the Applicant was able to observe thatan anti-friction strip obtained by extruding a polymer mixturecomprising polystyrene and a polyethylene oxide of the Alkox 300 typehas sliding capacity which is always better than that of apublicly-available strip obtained under the same conditions but using amixture of polyethylene oxide and of polyethylene glycol; furthermore,it is remarkable that this difference becomes greater with increasingnumber of simulated shaving sequences.

With the anti-friction strip of the invention, there is a small decreasein sliding capacity that is fairly regular from one day to the next,whereas with the above-mentioned public-domain strip, a like decreaseoccurs, but on the third or fourth day, there is a sudden drop insliding capacity.

For fixing the anti-friction strips of the invention on shaving heads,the Applicant recommends using the ultrasonic welding technique. Inorder to verify the quality of ultrasonic welds between polystyrene andpolyethylene oxide, polystyrene plates were welded to plates extrudedfrom a mixture of 60% polyethylene oxide and 40% polystyrene. To verifythe quality of the welding, the plate extruded from polystyrene andpolyethylene oxide was fixed in a vice, the pure polystyrene plate wastaken hold of, and traction was applied to breakage. Either the breaktook place through the weld proper, or else the break took place in theplate of polystyrene and polyethylene oxide. A weld is generallyconsidered to be of good quality if the major part of the break takesplace in the plate and not in the weld.

The table below gives the results obtained with the above-mentionedAlkox 160, 240, and 300 products. An additional test was performed usingAlkox E 100 whose molecular weight as specified by the manufacturer liesin the range 2.5 million and 3 million. As can be seen, with Alkox E100, the quality of the weld is less good insofar as all of the breaksare located in the weld proper and not in the material. Furthermore,there is a very large difference as to the mean force in kilogramsweight required to break the strip obtained from Alkox E 30 100 comparedwith the mean forces required for Alkox E 160, E 240, and E 300, whichgive results that are very close to one another. The best resultsconcerning coefficient of dynamic friction and concerning suitabilityfor ultrasonic welding were obtained with the anti-friction strip madeby extruding a mixture of 40% by weight polystyrene and 60% by weightpolyethylene oxide having a molecular weight lying in the range 7million to 8 million, said strip being ultrasonically welded to ashaving head made of polystyrene.

Number of breaks Type of Mean force in the weld polyethylene oxide (kg)(on 4 samples) Alkox E 100 12.9 4/4 Alkox E 160 20.8 2/4 Alkox E 24021.6 1/4 Alkox E 300  21.67 0/4

The preferred anti-friction strip of the invention which gives the bestresults both in terms of sliding capacity and durability of saidcapacity, and also in terms of manufacturing quality, is a strip whichis obtained by extruding a polymer mixture having about 30% polystyreneand about 70% polyethylene oxide with a mean molecular weight of morethan 7 million. The extruded mass is more compact than with polyethyleneoxides of lower molecular weight, thus making it possible to obtain astrip whose profile is more accurate and more regular.

In a preferred embodiment, using Alkox 300 (mean molecular weight in therange 7 million to 8 million), the mixture comprised 66.5% Alkox 300,32% polystyrene, and 1.5% additives, in particular colored pigments.

In addition to the above-mentioned characteristic polymer materials, theanti-friction strip of the invention can naturally also contain shavingadditives, in particular those mentioned in U.S. Pat. No. 4,170,821:cleaning agents, pharmaceutical agents, cosmetic agents, and coagulatingagents.

What is claimed is:
 1. An anti-friction strip for a discardable razor,the strip being obtained by extruding a polymer mixture comprising aninsoluble polymer material and polyethylene oxide, the strip beingcharacterized by an initial coefficient of dynamic friction (K_(D)) ofthe order of or less than 0.2, and by the fact that the mixture to beextruded comprises, as its polyethylene oxide, only a substance whosemean molecular weight is greater than 3.5 million.
 2. An anti-frictionstrip according to claim 1, characterized in that it is obtained byextruding a mixture comprising polystyrene and a polyethylene oxidehaving a mean molecular weight greater than 4 million.
 3. A shaving headhaving an anti-friction strip according to claim 2 fixed thereto byultrasonic welding.
 4. An anti-friction strip according to claim 2,characterized in that it is obtained by extruding a mixture ofpolystyrene and a single polyethylene oxide having a molecular weightgreater than 7 million.
 5. A shaving head having an anti-friction stripaccording to claim 4 fixed thereto by ultrasonic welding.
 6. Ananti-friction strip according to claim 4, characterized in that it isobtained by a mixture of about 30% polystyrene and about 70% of a singlepolyethylene oxide having a molecular weight greater than 7 million. 7.An anti-friction strip according to claim 6, wherein the polymer mixturecomprises 40% polystyrene and 60% polyethylene oxide and wherein thepolyethylene oxide has a molecular weight lying in the range of 7million to 8 million.
 8. A shaving head having an anti-friction stripaccording to claim 6 fixed thereto by ultrasonic welding.
 9. Ananti-friction strip according to claim 6, characterized in that it isobtained from a mixture of 32% polystyrene, 66.5% polyethylene oxidehaving a molecular weight lying in the range 7 million to 8 million, and1.5% additive.
 10. An anti-friction strip according to claim 9, whereinthe additive comprises a colored pigment.
 11. A shaving head having ananti-friction strip according to claim 9 fixed thereto by ultrasonicwelding.
 12. A shaving head having an anti-friction strip according toclaim 1 fixed thereto by ultrasonic welding.
 13. A shaving headaccording to claim 12, in which the portion on which the anti-frictionstrip is fixed is made of polystyrene.
 14. An anti-friction stripaccording to claim 1, wherein the polymer mixture further comprises ashaving additive.
 15. An anti-friction strip according to claim 14,wherein the shaving additive is a cleaning agent.
 16. An anti-frictionstrip according to claim 14, wherein the shaving additive is apharmaceutical agent.
 17. An anti-friction strip according to claim 14,wherein the shaving additive is a cosmetic agent.
 18. An anti-frictionstrip according to claim 14, wherein the shaving additive is acoagulating agent.